The present invention relates to vacuum furnaces and has particular application in the vacuum heating treating of work parts, wherein the work parts are introduced and processed in a subatmospheric environment and are thereafter removed from the furnace without closing down the operation of the furnace.
Prior to the instant invention, vacuum furnaces for heat treating and processing of metal articles have become generally accepted for commercial use; but, heretofore batch processing has been the generally accepted technique for use with vacuum furnaces; and, as a result, furnaces using the batch process have been somewhat limited in the use and application thereof. In this connection batch heat treating requires that the furnace be shut down after each heat treating cycle for removal of the processed work parts from the furance; and, although the results as obtained from such heat treating have been acceptable, it is understood that considerable time and labor is expended in shutting down the furnace, removing the parts therefrom, loading the furnace again, and then heat treating the new batch. Obviously, this technique is inefficient, since the furnace operation must be completely closed down during removal of the processed work parts and the introduction of the new parts therein.
Some efforts have been made heretofore to utilize continuously operated heat treating furnaces employing conveyor belts; but such furnaces have normally been usable in atmosphere environments, wherein an atmosphere has been introduced into the furnace heating chamber under pressure. In U.S. Pat. No. 3,782,705, a continuously operated vacuum furnace is disclosed; and, although the furnace as illustrated therein is capable of heat treating work parts without breaking the vacuum within the furnace, the door assemblies and conveyor mechanisms are somewhat complicated; and, therefore, the manufacture of such a furnace is relatively costly. Other attempts have been made to heat treat under vacuum in a continuously operated furnace, but problems have always been encountered in the loading of the work parts in the furnace and the unloading thereof without contaminating the furnace heating chamber.